It is known that blood is a very sensitive living liquid tissue and that it is readily altered when coming into contact with chemical substances or when exposed to mechanical stresses, for example shear stresses; it coagulates upon contact with most inert materials or during stases. In reality, very few hemocompatible materials exist and most of them require a patient carrying such hemocompatible material to take anticoagulants.
It is also known (see, for example, document U.S. Pat. No. 5,135,539) that cardiac prostheses exist in which the artificial ventricles comprise flexible membranes actuated by pulses of a fluid so as to cause movement of the blood. In this case, the hemocompatibility of said membranes is particularly essential, due to the fact that the membranes are mobile and in contact with a complex and often turbulent blood flow.
In the art, substantially hemocompatible materials which are either synthetic or of biological origin are known.
The synthetic materials are generally polyurethane elastomers or silicone elastomers; they are used either with a smooth surface, in order to reduce platelet or blood adhesions, or with a porous surface, in order to allow the adhesion of a biological layer capable of serving as an interface with the blood. Such synthetic materials have good qualities of flexibility, impermeability and deformability, but require the use of anticoagulants.
Material of biological origin includes, but is not limited to, animal tissue and biological material derived from animal tissue, for example collagen.
Tissues of animal nature have to be chemically fixed (most commonly with glutaraldehyde) when they are intended to be implanted into the human body, in order to prevent immunological reactions. Such biological materials thus treated generally have excellent hemocompatible properties and do not require, moreover, the use of anticoagulants, but they are absolutely not impermeable.
Conversely, “hemocompatible and implantable” synthetic materials generally have advantageous mechanical and leaktightness characteristics, but are tolerated in the blood stream only by means of a strict anticoagulation.
In order to be able to benefit from the good mechanical and leaktightness properties of synthetic materials and from the good hemocompatibility characteristics of materials of biological origin, document U.S. Pat. No. 5,135,539 envisions superimposing a membrane of synthetic material and a membrane of biological origin. However, such an arrangement leads to the formation of an intermediate chamber between said membranes, which can be the site of infections or of undesirable liquid collections.